The present invention relates to a servocontrol device for an erosion machine for regulating the erosion electrode with respect to a workpiece.
A servocontrol device of the type under consideration is already known, for example, from DE-OS No. 22 50 872. In the case of the known servocontrol device, a signal is generated indicating the position of the erosion electrode with respect to a workpiece, this signal being compared with a desired signal. The resulting error signal is supplied to a low pass filter circuit with a fixed cutoff frequency, which is connected on the output side to a driving circuit, which supplies with a driving current a driving device formed by an electromotor for the following up of the erosion electrode. In the known servocontrol device, the means for determining the actual or real distance between the erosion electrode and the workpiece establishes the distance from the ignition time lag between the processing voltage pulses and the processing current pulses.
As a function of the desired operation of the erosion machine, such as e.g. during roughing or during finishing, the frequency of the processing pulses can be varied from the megahertz range into a range of approximately 10 hertz.
Apart from the variation of the frequency of the processing pulses, during erosion, there is also a modification to the value for the optimum spacing between the erosion electrode and the workpiece as a function of different processing parameters, such as e.g. the current amplitude, the pulse duration, the no-load voltage, the conductivity of the liquid in the processing gap and the like. The change to the value for the optimum spacing between the erosion electrode and the workpiece is accompanied by a variation in the time within which it is necessary to carry out a correction of standard deviations from the desired value at a specific processing speed.
Thus, even in the case of erosion processing with a fixed, given frequency, changes take place to the remaining boundary conditions for the processing, so that the control circuit of the known servocontrol device with an invariable control characteristic is not able to satisfy in the same way all the process conditions which occur during the erosion process.